Thermoplastic sheet abrasives and methods of making the same

ABSTRACT

The present invention provides sheet abrasives that include a plurality of abrasive particles dispersed within a thermoplastic polymer. The present invention also provides methods for producing sheet abrasives.

FIELD OF THE INVENTION

The present invention relates generally to the field of sheet abrasives.More particularly, the invention relates to sheet abrasives comprisingabrasive particles dispersed within a thermoplastic polymer and methodsfor making the same.

BACKGROUND

Conventional sheet abrasives generally consist of abrasive particlesbonded to the surface of a paper or cloth base material. These types ofcoated sheet abrasives, however, suffer from several disadvantages.Typically, a coated sheet abrasive contains a single layer of abrasiveparticles coated on the base material, which itself is non-abrasive.During use, the abrasive particles are either worn down or becomedetached from the surface of the base material, leaving only bare basematerial in contact with the work surface. Thus, the useful life ofthese types of sheet abrasives is limited by the thickness of theabrasive particle layer and by the strength of the bond between theabrasive particles and the base material. In addition, the flexibilityof conventional coated sheet abrasives is limited because bending orstretching the sheets can dislodge the abrasive particles from the basematerial and crack, crease, or otherwise damage the sheet.

Abrasive sheets made of abrasive particles dispersed within a polymerare known. In some cases, these sheets are formed by mixing the abrasiveparticles and the polymer in an organic solvent, and subsequentlyevaporating the solvent. Storing, handling, and transporting the organicsolvents used in this process pose a significant inconvenience andhealth hazard to operators. Furthermore, evaporating the organicsolvents can make the process more costly and time consuming.

In other cases, abrasive particles are mixed with a polymer in solidform, and the mixture is compression molded to form a pad with aplurality of abrasive protrusions. The compression molding process istime consuming because the process in non-continuous, i.e., each moldcan only produce one abrasive pad at a time.

Therefore, there is a need for flexible sheet abrasives having increaseddurability and mechanical strength that can be produced in an efficient,cost-effective manner.

SUMMARY OF THE INVENTION

The present invention provides a sheet abrasive that includes aplurality of abrasive particles dispersed within a thermoplastic polymerlayer. The thermoplastic polymer layer preferably is an extrudedthermoplastic polymer layer or an injection-molded thermoplastic polymerlayer. The thermoplastic polymer layer makes the sheet abrasive strongyet flexible, and the abrasive particles are held firmly in place withinthe polymer layer without the need for an additional bonding material.Furthermore, because the abrasive particles are dispersed throughout thethickness of the thermoplastic polymer layer, not just on its surface,the sheet abrasive maintains its abrasive qualities even after itstopmost layer has been worn away.

The thermoplastic polymer layer can include, but is not limited to,polyamides, polyurethanes, acetals, thermoplastic polyimides, liquidcrystal polymers, polyphenylene sulfides, polyetheramides,polyetheresters, polyethylene, or combinations thereof. In addition, thethermoplastic polymer layer may be a foamed polymer. The thermoplasticpolymer may be an extruded thermoplastic polymer or an injection-moldedthermoplastic polymer. The extruded thermoplastic polymer layer can beuni-axially or bi-axially oriented. The sheet abrasive preferably has athickness ranging from about 0.001 inch to 0.25 inch.

The abrasive particles can include, but are not limited to, siliconcarbide, aluminum oxide, diamond, ceramic aluminum oxide, ceramic,zirconia aluminum, garnet, cubic boron nitride, talc, and combinationsthereof. The abrasive particles can be dispersed substantially uniformlywithin the thermoplastic polymer layer. The abrasive particles cancomprise from about 1% to about 30% by volume of the sheet abrasive.

The sheet abrasive can contain a second layer, such as a polymer layer,adjacent to the thermoplastic polymer layer. The second layer also maycontain a plurality of abrasive particles. An adhesive layer may bedisposed between the thermoplastic polymer layer and the second layer.Sheet abrasives of the invention can be adapted to form a continuousbelt or a flap wheel.

The present invention also provides methods of forming sheet abrasivesof the invention that include the steps of dispersing a plurality ofabrasive particles in a thermoplastic polymer and either extruding thethermoplastic polymer to form an extruded thermoplastic polymer layer orinjecting the thermoplastic polymer into a mold to form aninjection-molded thermoplastic polymer layer. The thermoplastic polymerlayer preferably is extruded or molded to a thickness ranging from about0.001 inch to 0.25 inch. An extruded thermoplastic polymer layer can beoriented either uni-axially or bi-axially, for example, by stretching.

A second layer can be provided adjacent to the thermoplastic polymerlayer. The second layer can be a polymer and/or contain a plurality ofabrasive particles. The second layer can be co-extruded with an extrudedthermoplastic polymer layer, or the second layer can be adhered to theextruded thermoplastic polymer layer with an adhesive. The second layercan be co-molded with an injection-molded thermoplastic polymer layer,or the second layer can be present within the mold prior to injectingthe molten thermoplastic polymer, or the second layer can be adhered tothe injection-molded thermoplastic polymer layer with or without anadhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the appended claims.The advantages of the invention can be better understood by reference tothe description taken in conjunction with the accompanying drawings.

The drawings are not necessarily to scale, emphasis instead generallybeing placed upon illustrating the principles of the invention. In thedrawings, like reference characters generally refer to the same partsthroughout the different views.

FIG. 1A is a schematic cross-sectional views of an embodiment of a sheetabrasive.

FIG. 1B is a schematic cross-sectional view of the sheet abrasive ofFIG. 1A after use.

FIG. 2 is a schematic cross-sectional view of another embodiment of asheet abrasive.

FIG. 3 is a schematic cross-sectional view of an embodiment of a sheetabrasive that includes a thermoplastic polymer layer and a second layer.

FIG. 4 is a schematic representation of an embodiment of an extruder forproducing sheet abrasives.

DETAILED DESCRIPTION

Throughout the description, where compositions are described as having,including, or comprising specific components, or where processes aredescribed as having, including, or comprising specific steps, it iscontemplated that compositions of the invention also consist essentiallyof, or consist of, the recited components, and that the processes of theinvention also consist essentially of, or consist of, the recited steps.

As illustrated by FIG. 1A, a sheet abrasive 2 according to oneembodiment of the invention includes a plurality of abrasive particles4A, 4B dispersed within a thermoplastic polymer layer 6. The abrasiveparticles can be dispersed substantially uniformly throughout thethickness of the thermoplastic polymer layer, or they can be dispersedin a non-uniform fashion. For example, the concentration of abrasiveparticles may be greater near one or more surfaces of the thermoplasticpolymer layer.

Wither reference to FIG. 1A, a portion of the abrasive particles may belocated at or near a surface 8 of the thermoplastic polymer layer 6(e.g., abrasive particle 4A in FIG. 1A) with other abrasive particleslocated in the interior 10 of the thermoplastic polymer layer 6 (e.g.,abrasive particle 4B in FIG. 1A). During use, friction between thesurface of the sheet abrasive and a work surface wears away portions ofthe thermoplastic polymer layer and any abrasive particles embeddedtherein. As the thermoplastic polymer layer 6 is worn away, an abrasiveparticle 4B that was previously in the interior 10 of the thermoplasticpolymer layer 6 is exposed, as illustrated by FIG. 1B. Thus, unlikeconventional coated sheet abrasives, which are no longer useful oncetheir topmost abrasive layers have worn away, a sheet abrasive of theinvention maintains its abrasive qualities after portions of thethermoplastic polymer layer are worn away, thereby increasing the usefullife of the sheet abrasive.

In some embodiments of a sheet abrasive, a portion of the abrasiveparticles are located at more than one surface of the thermoplasticpolymer layer. For example, in the illustrative embodiment shown in FIG.2, the abrasive particle 4A is located at one surface 8 of thethermoplastic polymer layer 6, and the abrasive particle 4C is locatedat the other surface 12. The remaining abrasive particle 4B is locatedin the interior 10 of the thermoplastic polymer layer 6. In thisembodiment, both surfaces 8, 12 of the sheet abrasive 2 can perform workon one or more work surfaces.

The thermoplastic polymer layer can be any thermoplastic polymer knownin the art. Suitable materials include, for example, polyamides,polyesters, polyoxymethylenes, polyethylene, ethylene copolymers,ethylene acrylic acid copolymers, ethylene acrylate copolymers, ethylenemethacrylic acid copolymers, ethylene vinyl alcohol copolymer, ethylenevinyl acetate copolymers, polyphenylene ether, polyphenylene oxide,polyphthalamide, polypropylene, polystyrene, polyacrylonitrile,polyurethanes, rubbery polymers (such as, for example, ethylenepropylene rubbers and ethylene propylene diene rubbers), polyvinylchloride, styrene acrylonitrile, acrylonitrile butadiene styrene,styrene butadiene, styrene maleic anhydride, polycarbonate,polyurethanes, acetals, acrylics, cellulosics, cellulose acetatebutyrate, cellulose acetate propionate, fluoropolymers (such as, forexample, polyvinylidene fluoride (PVDF), perfluoroalkoxy (PFA), ethylenetetrafluoroethylene (ETFE), fluorinated ethylene propylene (FEP),chlorotrifluoroethylene (CTFE), and polytetrafluoroethylene (PTFE)),ionomers, liquid crystal polymers, polyphenylene sulfide, polyamideimide, thermoplastic polyimides, polyarylate, polybutylene,polyaryletherketone, polyetherether ketone, polyetherketones,polyetherimides, polyethersulfone, polysulfone, thermoplasticelastomers, polyetheramides, polyetheresters, diallyl phthalate,melamine phenolic, phenolics, and unsaturated polyesters.

Alternatively, the thermoplastic polymer layer can include acombination, blend or alloy of one or more polymers as described above.Polymer blends or alloys can include one or more polymers suspended inanother polymer, one or more polymers dissolved in another polymer, or amixture of suspended and dissolved polymers. The blends or alloys can bemiscible or immiscible. Sheet abrasives can also be formulated such thatthe thermoplastic polymer layer can be subsequently cross-linked orcured in a secondary operation, if desired, in order to maximize certainproperties such as heat resistance, toughness or elasticity.

In some embodiments, the thermoplastic polymer layer is foamed. Foamingmakes the thermoplastic polymer lightweight and shock-absorptive. Onemethod for foaming a polymer is by the addition of one or more blowingagents to the polymer prior to forming an abrasive sheet. A blowingagent is a solid or a fluid that causes bubbles, for example, gasbubbles, to form within the polymer, which expand as the molten polymercools. Examples of blowing agents include foaming agents such asFoamazol® 72 and Foamazol® XO-227 (Bergen International, Rochelle Park,N.J.). Gaseous blowing agents include inert gases such as nitrogen andargon.

The abrasive particles generally have a Knoop scale hardness value thatis greater than the thermoplastic polymer layer. Suitable materialsinclude, for example, aluminum oxide, silicon carbide, zirconiaaluminum, ceramic aluminum oxide, natural and artificial diamond, glassbeads, calcium oxide, talc, clay, ceramic, fiberglass, silica, woodfillers, nut shells, apatite, feldspar, tool steel, quartz, chromium,zirconium, beryllia, topaz, garnet, zirconium boride, titanium nitride,tungsten carbide, tantalum carbide, zirconium carbide, alumina,beryllium carbide, titanium carbide, silicon carbide, aluminum boride,cubic boron carbide, cubic boron nitride, emery, spinel, flint, andmixtures thereof.

One example of a suitable mixture of abrasive particles is a mixture ofsilicon carbide and aluminum oxide. In addition, aggregates or multipleabrasive particles fused together by a bonding agent can be used. Theabrasive particles may be completely or partially coated by an inorganicor metallic coating material. Examples include nickel-coated diamond andcopper-coated diamond. The abrasive particles may be coated with acoupling agent, such as a silane coupling agent (e.g.,3-aminopropyl-triethoxysilane) to increase the adhesion of the abrasiveparticles to the thermoplastic polymer layer. The abrasive particles canhave any size or shape, although preferably the abrasive particles aresmall enough to be contained entirely within the thickness of thethermoplastic polymer layer. Mixtures of different sized of abrasiveparticles can be used, such as, for example, a mixture of 46 mesh and120 mesh silicon carbide.

The abrasive particles can comprise from about 1% to about 50% by volumeof the thermoplastic sheet abrasive, from about 1% to about 40% byvolume of the thermoplastic sheet abrasive, or from about 1% to about30% by volume of the thermoplastic sheet abrasive. In some embodiments,the abrasive particles comprise up to 25% by volume, or up to 35% byvolume, or up to 45% by volume of the thermoplastic sheet abrasive. Theamount of abrasive particles found in sheet may be higher than 50% byvolume depending on the particular characteristics of the abrasiveparticles and/or the thermoplastic polymer used to form thethermoplastic sheet abrasive.

In addition to abrasive particles, one or more additives known in theart can be included in a sheet abrasive. Examples of additives includecolorants, tougheners (including rubber tougheners), plasticizers,fillers, reinforcements, lubricants, anti-blocking compounds, processaids, stabilizers, and blowing agents.

Sheet abrasives in accordance with the invention can be produced by anyconventional thermoplastic processing method, including molding andextrusion. It should be understood that in any of the methods describedand claimed herein, the steps can be performed in any order, or one ormore steps can be performed simultaneously, as long as the methodremains operable.

In a preferred method, sheet abrasives are produced by an extrusionmethod. Extrusion methods can produce sheet abrasives of any length, andthe sheets can conveniently be wound onto rolls. The extrusion processgenerally involves adding one or more thermoplastic polymers, abrasiveparticles, and any additional polymers and/or additives into athermoplastic melt-mixing device. The components are transported throughthe device, for example, using a screw, toward a die which is cut in theshape of the desired product. As the thermoplastic polymer(s) movewithin the device, they begin to melt into a softer flowing material andmix with the other components. The molten thermoplastic polymer mixtureis forced through the die, yielding a polymer extrudate. The extrudatethen is quenched or solidified, typically using a rollstack device.Alternatively, the extrudate may be quenched or solidified using air ora water bath. Additional finishing steps may include removing excesswater using an air blower and/or threading the extrudate through pinchrolls to control its width or diameter. After quenching, the sheetabrasive can be cut to desired lengths and/or wound onto rolls.

Examples of suitable extrusion devices include single-screw extruders,twin-screw extruders, brabender type mixers, and kneaders, some of whichare commercially available from Battenfeld Gloucester (Gloucester,Mass.) and Davis Standard (Pawcatuck, Conn.). The surfaces of theextruder and other processing equipment that come into contact with thesheet abrasives can be modified with hardened surfaces or liners toprevent wear and increase the useful life of the extruder.

In some embodiments, after the sheet abrasive has been extruded andquenched or solidified, it is subjected to an orientation process toincrease the tensile strength of the sheet. Orientation generallyinvolves stretching or compressing the sheet abrasive at a temperatureabove the polymer's glass transition temperature, but below itscrystalline melting temperature. Orientation can be uni-axial, typicallyby stretching or compressing the sheet along its length (i.e., in thecasting machine direction), or bi-axial, typically by also stretching orcompressing the sheet in a transverse direction (i.e., in a crossmachine direction). Bi-axial orientation is typically done using atenter frame or compression or nip rolls. In some embodiments, theentire sheet abrasive can be oriented, while in other embodiments, oneor more portions of the sheet abrasive are oriented and other portionsare not. Suitable equipment for orienting sheet abrasives iscommercially available from Marshall and Williams Plastics (Woonsocket,R. I.), Battenfeld Gloucester (Gloucester, Mass.), and Davis Standard(Pawcatuck, Conn.).

Molded sheet abrasives preferably are prepared by compression orinjection molding. In compression molding, a thermoplastic polymer isplaced into a mold which is subsequently closed and held at a highpressure. The mold is heated to fuse the thermoplastic polymer, andafter an appropriate time, the mold is opened and the product removed.In contrast, injection molding involves injecting a molten thermoplasticpolymer into a closed mold. The molten polymer cools and hardens intoshape within the mold, which then is opened to remove the product. Anymaterials and methods used in compression or injection molding known inthe art may be used to form sheet abrasives in accordance with theinvention.

The cross-sectional shape of a sheet abrasive can be tailored to suitits particular application. In some embodiments, the sheet abrasive hasthe form of a film, strip, or tape, i.e., its width and length aregreater than its thickness. However, thermoplastic abrasives can beformed into any shape to adapt to any particular application, forexample, a block or o-ring shape. For sheet abrasives produced by anextrusion process, the cross-sectional shape is determined by the shapeof the extrusion die. For a molding process, the shape of the molddetermines the cross-sectional shape of sheet abrasives. In eitherprocess, the cross-sectional shape can be further modified by thermal,chemical, and/or mechanical means after the thermoplastic polymer hasbeen extruded or molded. A sheet abrasive can have any cross-sectionalshape, including, for example, quadrilateral, round, and oval.

In some embodiments, a sheet abrasive according to the invention has athickness ranging from about 0.0005 inch to about 0.25 inch. In otherembodiments, a sheet abrasive has a thickness ranging from about 0.001inch to about 0.25 inch, or from about 0.001 inch to about 0.125 inch.In other embodiments, a sheet abrasive has a thickness ranging fromabout 0.001 inch to about 0.05 inch. In still other embodiments, a sheetabrasive has a thickness ranging from about 0.005 inch to about 0.03inch.

In the illustrative embodiment shown in FIG. 3, a sheet abrasive 20includes a second layer 22 adjacent to a thermoplastic polymer layer 24which contains a plurality of abrasive particles 26. The second layercan serve to enhance various properties of the abrasive sheet,including, for example, stiffness, toughness, resilience, abrasionresistance, coefficient of friction, heat stability, chemicalresistance, hydrolysis resistance, oxidative stability, heatconductivity, anti-static properties, electrical conductivity, and/orthermal coefficient of expansion. The second layer can be made of anymaterial, including, for example, paper, cloth, metal, polymer, orcombinations thereof. The second layer can have various forms,including, for example, a continuous sheet, a fibrous woven or non-wovenbelt, a web or mesh, or a layer of abrasive particles.

Suitable metals for use in a second layer include, for example,aluminum, chromium, steel, and alloys thereof. Any of the polymers orcombination of polymers described above in connection with thethermoplastic polymer layer can be used to form the second layer. Inaddition, the second layer can include any of the abrasive particlesand/or additives described above. In some embodiments, the second layercontains the same type and/or amount of abrasive particles and/oradditives as the thermoplastic polymer layer. In other embodiments, thesecond layer and the thermoplastic polymer layer contain different typesand/or amounts of abrasive particles and/or additives.

The second layer can be bonded to the thermoplastic polymer layer usingan adhesive, or the second layer can be coated or sprayed onto to thethermoplastic polymer layer. In cases where the second layer includes apolymer, the second layer can be extruded onto the thermoplastic polymerlayer, or the second layer and an extruded thermoplastic polymer layercan be co-extruded. A co-extrusion process involves extruding two ormore layers simultaneously by combining the extrudates from multipleextruders into a manifold and extruding through a special multi-layerdie. Alternatively, the second layer can be present within a mold priorto injecting a molten thermoplastic layer into the mold. Each layer canhave the same or different widths, and the layers may be offset.

The second layer can have the same thickness as the thermoplasticpolymer layer, or the two layers can have different thicknesses. Thatis, the thermoplastic polymer layer can have a thickness greater thanthe thickness of the second layer, or the thermoplastic layer can have athickness less than the thickness of the second layer. The second layerand the thermoplastic polymer layer can have the same shape and/or size,or their shapes and/or sizes may differ.

In some embodiments, the second layer and the thermoplastic polymerlayer are aligned so that the second layer is adjacent to substantiallyall of a surface of the thermoplastic polymer layer. In otherembodiments, the second layer and the thermoplastic polymer layer areoffset, so that at least one portion of the thermoplastic polymer layeris not adjacent to the second layer. This embodiment is particularlyuseful for sheet abrasives that are extruded and wound into rolls.

The present invention also contemplates sheet abrasives that containfurther layers in addition to a thermoplastic polymer layer and a secondlayer. For example, a sheet abrasive may include a third layer, a fourthlayer, a fifth layer, a sixth layer, a seventh layer, an eighth layer,and so on. The additional layers can be disposed adjacent to any otherlayer. For example, in a sheet abrasive that contains a thermoplasticpolymer layer, a second layer, and a third layer, the third layer can beadjacent to either the thermoplastic polymer layer or the second layer.The additional layers can have some or all of the characteristics andproperties described above for the second layer and can be made by thesame processes and techniques described above.

Sheet abrasives in accordance with the invention can be used in avariety of ways similar to conventional coated abrasives, such as emerycloth or sand paper. In addition, the sheet abrasives can bethermoformed into a variety of shapes heretofore unobtainable withconventional coated abrasives to create new tools engineered to fitspecific applications.

Thermoforming involves applying heat and/or pressure to a sheet abrasiveto form the sheet into a different three-dimensional shape. For example,in one embodiment according to the invention, a thermoplastic sheetabrasive is thermoformed to fit over the end of a pipe (e.g., similar tothe shape of a lid for a disposable drinking cup). The resultingthermoformed abrasive then can be used as a de-burring or polishing toolfor the end of like-sized metal pipes.

In one embodiment, an adhesive polymer layer is disposed between athermoplastic polymer layer containing a plurality of abrasive particlesand a second layer that provides reinforcement, toughening or otherattributes. In a variation of this embodiment, the second layer is aremovable backing or liner, which, when removed, exposes the adhesivelayer which remains disposed on the thermoplastic polymer layer. Thesheet abrasive can then be adhered to another surface using the adhesivelayer. In a related embodiment, the second layer is a fastening system,for example, a hook and loop device (e.g., Velcro®), which can be usedto fasten the sheet abrasive to another surface.

In other embodiments of a sheet abrasive, the thermoplastic polymerlayer includes a thermoplastic elastomer, such as, but not limited to,soft polyurethanes, polyetheresters, or polyetheramide esters. The sheetabrasive is very flexible and can be used on curved surfaces (e.g.,contours of molding, metal rods, etc.) that cannot effectively be sandedby conventional coated abrasives.

In some embodiments, the second layer is foamed to provide for shockabsorption, insulation, or sound damping qualities. In otherembodiments, the second layer includes fiberglass or clay to provideenhanced stiffness. The second layer may include a high thermalconductivity filler to enhance cooling of the sheet abrasive. In otherembodiments, the second layer includes tungsten or other high densityfillers to provide a sheet abrasive with increased weight for use inflapwheel-type applications. In yet other embodiments, an intermediatelayer is extruded between two thermoplastic polymer layers containing aplurality of abrasive particles to produce an abrasive sheetconstruction with abrasive on the top and bottom with a reinforcing ortoughening layer in between. It is to be understood that, in addition tothe embodiments described above, a sheet abrasive in accordance with thepresent invention can have any configuration of thermoplastic polymerlayer, second layer, and/or additional layers.

Sheet abrasives in accordance with the invention can be cut to anydesired length or shape and used directly, like conventional sand paper,or they can be formed into implements or tools. For example, a sheetabrasive can be cut and the ends joined using conventional bonding orjoining techniques to form belts. Alternatively, a sheet abrasive can becut into flaps and formed into star pads, cross pads, square pads, flapwheels, flap discs, cartridge rolls, spiral bands, overlap discs,overlap cones, and other implements known in the art. Examples ofimplements that can be formed using sheet abrasives according to theinvention can be found in the catalogue, “3M Grindline Express CoatedAbrasive, Surface Conditioning, and Superabrasive Products 1996” (3MCompany, Minneapolis, Minn.).

EXAMPLES

The following examples are meant to illustrate, not limit, the scope ofthe present invention.

Example 1

All examples were produced using the extruder 30 illustratedschematically in FIG. 4. The polymer starting materials were added tothe rear of the extruder 30 through primary feeder 32, and the abrasiveparticles were added through secondary feeder 34. The extrudate 36exited the die 38 vertically downward into a water quench bath 40 wherethe extrudate 36 was solidified. A standard 6 inch film type die 38 withan adjustable die gap (Extrusion Dies Inc., Chippewa Falls, Wis.) wasused. The die gap was set at 0.058 inch for all examples. The extrudate36 was pulled by a set of slow group orientation rolls 42, and waspassed through an orientation oven 44 and then onto a set of fast grouporientation rolls 46. Next, the extrudate 36 was passed through arelaxation oven 48, a set of crimp rolls 50 to provide crimp, and thenthrough a set of lube rolls 52 coated with a lubricant. The extrudate 36then was passed onto a set of relaxation group rolls 54, which were setat the same speed as the fast group orientation rolls 46. Finally, theextrudate 36 was wound onto a collection reel 56.

The extrusion conditions are listed in Table 1. Samples A, B, C, D andthe control sample included nylon 6 (Ultramid® B3 Natural, BASF,Ludwigschafen, Germany), and samples E and F included nylon 6/12 (Zytel®158, DuPont, Wilmington, Del.). All nylons were dried for four hours at175° F. for four hours just prior to extrusion. All samples except forthe control included 120 mesh aluminum oxide abrasive particles (NortonAbrasives, Worcester, Mass.). The compositions are listed in weightpercent as determined by pyrolysis and gravimetric analysis of theresidual aluminum oxide. TABLE 1 Control Sample A Sample B Sample CSample D Sample E Sample F Polymer 100% 60% 60% 54% 54% 40% 40% Nylon 6Nylon 6 Nylon 6 Nylon 6 Nylon 6 Nylon Nylon 6/12 6/12 Abrasive  0% 40%40% 46% 46% 60% 60% Extruder Temp. Zone 1 514° F. 514° F. 514° F. 514°F. 514° F. 514° F. 514° F. Zone 2 516° F. 516° F. 516° F. 516° F. 516°F. 516° F. 516° F. Zone 3 511° F. 511° F. 511° F. 511° F. 511° F. 511°F. 511° F. Zone 4 500° F. 500° F. 500° F. 500° F. 500° F. 500° F. 500°F. Zone 5 511° F. 511° F. 511° F. 511° F. 511° F. 511° F. 511° F. Zone 6504° F. 504° F. 504° F. 504° F. 504° F. 504° F. 504° F. Zone 7 518° F.518° F. 518° F. 518° F. 518° F. 518° F. 518° F. Zone 8 523° F. 523° F.523° F. 523° F. 523° F. 523° F. 523° F. Zone 9 511° F. 511° F. 511° F.511° F. 511° F. 511° F. 511° F. Zone 10 509° F. 509° F. 509° F. 509° F.509° F. 509° F. 509° F. Zone 11 500° F. 500° F. 500° F. 500° F. 500° F.500° F. 500° F. Zone 12 500° F. 500° F. 500° F. 500° F. 500° F. 500° F.500° F. Zone 13 510° F. 510° F. 510° F. 510° F. 510° F. 510° F. 510° F.Die Temp. 520° F. 520° F. 520° F. 520° F. 520° F. 520° F. 520° F.Extruder 38 38 38 38 38 38 38 RPM Roller Speed (RPM) Slow group 79 79 7272 79 80 80 Fast group 104 104 144 144 104 80 88 Relaxation 104 104 144144 104 80 88 group Orientation 1.3 1.3 2.0 2.0 1.3 1.0 1.1 Ratio Sheet0.007 0.016 0.015 0.015 0.017 0.025 0.024 Thickness (inches)

Test strips (1.0 inch wide by 12 inches long) of each sample wereprepared. For comparative purposes, a test strip made from a commercialnon-woven abrasive strip, Standard B/T Belt, SCF-FE containing 120 meshaluminum oxide (Standard Equipment Company, Mobile, Ala.), was alsoprepared. Each test strip was rubbed for 6 strokes (3 in each direction)using light hand pressure (about 5 lbs. or off-hand application) over a1.5 inch diameter copper pipe. The contact length on the pipe wascontrolled at 2 inches, with 5 inches of each test strip contacting thepipe. The polishing ability of each sample was ranked from 0 to 5, with0 being poor or no polish and 5 being high polish. The test results areshown in Table 2.

Referring to Table 2, the control sheet which contained no abrasiveparticles had no polishing affect on the copper pipe. The commercialabrasive strip produced very modest polishing results, while samples A-Fproduced good polishing results. The polishing results appeared toimprove in proportion to the percent of abrasive particles in thestrips. This experiment demonstrates that sheet abrasives in accordancewith the present invention can produce polishing results comparable withor better than commercially available non-woven abrasive materials.TABLE 2 Sample Polymer % Abrasive Polishing Rank Control Nylon 6 None 0Standard B/T Belt SCF-FE Unknown 1 SCF-FE A Nylon 6 40% 3 B Nylon 6 40%2 C Nylon 6 46% 3 D Nylon 6 46% 3.5 E Nylon 6/12 60% 4 F Nylon 6/12 60%4

Example 2

A two layer sheet abrasive sample was prepared by adhering a controlsheet made of nylon 6 onto sample F using hot melt glue. The resultingtwo-layer sheet abrasive sample could not be torn by hand, while SampleE, which did not contain a second layer, could be torn with moderateeffort. This experiment demonstrates sheet abrasives that include two ormore layers can exhibit improved mechanical properties, such as improvedtensile strength.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments are therefore to be considered in all respects illustrativerather than limiting on the invention described herein. Scope of theinvention is thus indicated by the appended claims rather than by theforegoing description, and all changes that come within the meaning andrange of equivalency of the claims are intended to be embraced therein.

1. A sheet abrasive comprising: a thermoplastic polymer layer; and aplurality of abrasive particles dispersed therein.
 2. The sheet abrasiveof claim 1, wherein the thermoplastic polymer layer is selected from thegroup consisting of polyamides, polyurethanes, acetals, thermoplasticpolyimides, liquid crystal polymers, polyphenylene sulfides,polyetheramides, polyetheresters, and polyethylene.
 3. The sheetabrasive of claim 1, wherein the plurality of abrasive particles isselected from the group consisting of silicon carbide, aluminum oxide,diamond, ceramic aluminum oxide, ceramic, zirconia aluminum, garnet,cubic boron nitride, and talc.
 4. The sheet abrasive of claim 1, whereinthe polymer layer has a thickness from about 0.001 inch to about 0.25inch.
 5. The sheet abrasive of claim 1, wherein the plurality ofabrasive particles is dispersed substantially uniformly within thethermoplastic polymer layer.
 6. The sheet abrasive of claim 1, whereinthe thermoplastic polymer layer is an extruded thermoplastic polymerlayer.
 7. The sheet abrasive of claim 6, wherein the extrudedthermoplastic polymer layer is uni-axially oriented.
 8. The sheetabrasive of claim 6, wherein the extruded thermoplastic polymer layer isbi-axially oriented.
 9. The sheet abrasive of claim 1, wherein thethermoplastic polymer layer is an injection-molded thermoplastic polymerlayer.
 10. The sheet abrasive of claim 1, wherein the thermoplasticpolymer layer comprises a foamed thermoplastic polymer.
 11. The sheetabrasive of claim 1, wherein the abrasive particles comprise from about1% to about 30% by volume of the sheet abrasive.
 12. The sheet abrasiveof claim 1, wherein the abrasive sheet is adapted to form a continuousbelt.
 13. The sheet abrasive of claim 1, wherein the abrasive sheet isadapted to form a flap wheel.
 14. The sheet abrasive of claim 1, furthercomprising a second layer adjacent to the thermoplastic polymer layer.15. The sheet abrasive of claim 14, wherein the second layer comprises apolymer.
 16. The sheet abrasive of claim 14, wherein the second layerfurther comprises a plurality of abrasive particles.
 17. The sheetabrasive of claim 14, further comprising an adhesive layer disposedbetween the thermoplastic polymer layer and the second layer.
 18. Thesheet abrasive of claim 14, wherein the abrasive sheet is adapted toform a continuous belt.
 19. The sheet abrasive of claim 14, wherein theabrasive sheet is adapted to form a flap wheel.
 20. A method of forminga sheet abrasive comprising the steps of: dispersing a plurality ofabrasive particles in a molten thermoplastic polymer; and extruding themolten thermoplastic polymer to form a sheet abrasive, wherein the sheetabrasive comprises an extruded thermoplastic polymer layer and theplurality of abrasive particles dispersed therein.
 21. The method ofclaim 20, wherein the thermoplastic polymer is extruded to form anextruded thermoplastic layer having a thickness from about 0.001 inch toabout 0.25 inch.
 22. The method of claim 20, comprising orienting theextruded thermoplastic polymer layer in a uni-axial or bi-axialdirection.
 23. The method of claim 22, wherein the orienting stepcomprises stretching the extruded thermoplastic polymer layer.
 24. Themethod of claim 20, further comprising the step of providing a secondlayer adjacent to the extruded thermoplastic polymer layer.
 25. Themethod of claim 24, wherein the second layer further comprises aplurality of abrasive particles.
 26. The method of claim 24, wherein thesecond layer comprises a polymer.
 27. The method of claim 26, whereinproviding the second layer comprises co-extruding the extrudedthermoplastic polymer layer and the second layer.
 28. The method ofclaim 24, wherein providing the second layer comprises adhering thesecond layer to the extruded thermoplastic polymer layer with anadhesive.
 29. A method of forming a sheet abrasive comprising the stepsof: dispersing a plurality of abrasive particles in a thermoplasticpolymer; and injecting the thermoplastic polymer into a mold to form asheet abrasive, wherein the sheet abrasive comprises an injection-moldedthermoplastic polymer layer and the plurality of abrasive particlesdispersed therein.